GeoJSON strings should not include internal feature ids, r=bbinet (closes #3313)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12109 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Format/GeoJSON.js

@@ -530,12 +530,15 @@ OpenLayers.Format.GeoJSON = OpenLayers.Class(OpenLayers.Format.JSON, {
          */
         'feature': function(feature) {
             var geom = this.extract.geometry.apply(this, [feature.geometry]);
-            return {
+            var json = {
                 "type": "Feature",
-                "id": feature.fid == null ? feature.id : feature.fid,
                 "properties": feature.attributes,
                 "geometry": geom
             };
+            if (feature.fid != null) {
+                json.id = feature.fid;
+            }
+            return json;
         },
         
         /**